Fluid delivery for scanning probe microscopy

ABSTRACT

A gas (or fluid) is introduced around an SPM probe or Nanotool™ to control chemical activity e.g., oxygen to promote oxidation, argon to inhibit oxidation or clean dry air (CDA) to inhibit moisture to control static charging due to the action of the probe or nanotools and to provide vacuum at and around the tip and substrate area. Electrical current can be produced for use with active electronic devices on, in or near the body of the device. In addition by use of a fluid like water, certain oils, and other liquids in conjunction with specific tip structure either electric discharge machining can be used at the tip area on the tip itself (in conjunction with a form structure on the work piece) or on a work piece beneath the tip to shape, polish and remove material at very small scales (10 microns to 1 nm or less).

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/079,741, filed Apr. 4, 2011,

-   -   which is a continuation of U.S. application Ser. No. 12/399,165,        filed Mar. 6, 2009, now U.S. Pat. No. 7,930,766,    -   which is a continuation of U.S. application Ser. No. 11/244,312,        filed Oct. 4, 2005, now U.S. Pat. No. 7,503,206,    -   which is a divisional of U.S. application Ser. No. 10/659,737,        filed Sep. 9, 2003, now U.S. Pat. No. 6,998,689,    -   which claims priority from U.S. Provisional Application No.        60/409,403, filed Sep. 9, 2002 and from U.S. Provision        Application No. 60/433,242, filed Dec. 12, 2002,        all the disclosures of which are hereby incorporated by        reference in their entirety for all purposes.

This application is related to U.S. patent applications:

-   -   U.S. patent application Ser. No. 10/094,149, filed Mar. 7, 2002,        now U.S. Pat. No. 6,802,646;    -   U.S. patent application Ser. No. 10/094,411, filed Mar. 7, 2002;    -   U.S. patent application Ser. No. 10/094,408, filed Mar. 7, 2002,        now U.S. Pat. No. 6,923,044;    -   U.S. patent application Ser. No. 10/093,842, filed Mar. 7, 2002;        now U.S. Pat. No. 7,196,328;    -   U.S. patent application Ser. No. 10/094,148, filed Mar. 7, 2002,        now U.S. Pat. No. 6,752,008; and    -   U.S. patent application Ser. No. 10/228,681, filed Aug. 26,        2002, now U.S. Pat. No. 6,880,388        the disclosures of which are hereby incorporated by reference        for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to microelectromechanicalsystems (MEMS), and in particular to techniques for fluid delivery inapplications involving nanometer-scale operations, such as assays and/oramplification and subsequent modification of DNA in biochips. Inaddition this invention can be used to remove or add material viachemical, electro-chemical, biochemical, mechanical and electricalmethods in small controlled regions down to atomic dimensions of 0.1nanometer.

Nanometer-scale components find utility in a wide variety of fields,particularly in the fabrication of microelectromechanical systems(MEMS). Typical MEMS include micro-sensors, micro-actuators,micro-instruments, micro-optics, and the like. Nanotechnology refers tobroad categories of nanometer-scale manufacturing processes, materialsand devices, including, for example, nanometer-scale lithography andnanometer-scale information storage. Many MEMS fabrication processesexist, including, for example surface micromachining techniques. Surfacemicromachining involves fabrication of microelectromechanical systemsfrom films deposited on the surface of a substrate. For example, acommon fabrication process includes depositing thin layers ofpolysilicon on a sacrificial layer of silicon dioxide formed on a bulksilicon substrate. Controlled removal of the selected portions of thevarious layers of material can produce useful micro- and nano-scalemachine components.

Conventional semiconductor processing typically is performed in vacuum.The nature of the surrounding ambient is important. Often a dry ambientis required to avoid oxidizing and otherwise contaminating the surfaceof the silicon surface. Presently static conditions, vacuum generation,moisture problems and/or chemical reactivity control is obtained in SPM(scanning probe microscopy) systems and nanomachining centers by theintroduction of large quantities of gas (including CDA, clean dry air)at some distance many inches or more away from the probe subject site.These gross-scale manipulations of fluid are at odds with the fine-scaleoperations required in nanotechnology-based machining systems. To date,no suitable techniques exist to provide for more effective gas andvacuum delivery in the proximity of a site being worked by ananomachining process.

SUMMARY OF THE INVENTION

A micro electromechanical systems (MEMS) device is configured withfluidic channels to perform various tasks, including measuring andnanomachining a workpiece. One or more isotopic regions can be providedto further enhance the measuring function and to enhance nanomachiningoperations. The isotopic region(s) can provide power to a workpiece.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of an embodiment of a microelectro-mechanical systems (MEMS) cantilever according to one aspect ofthe present invention;

FIG. 1A shows a variation of the MEMS cantilever illustrated in FIG. 1;

FIG. 1B shows yet another variation of the MEMS cantilever illustratedin FIG. 1;

FIG. 1C shows a variation of the MEMS cantilever illustrated in FIG. 1B;

FIG. 2 is a schematic illustration of another embodiment of a MEMScantilever according to another aspect of the present invention;

FIG. 2A illustrates fluidic flow in accordance an embodiment of thepresent invention;

FIG. 2B is an exploded side view showing fluid flow in accordance withan embodiment of the present invention;

FIG. 2C is an exploded side view showing fluid flow in accordance withanother embodiment of the present invention;

FIG. 3 is a diagrammatic illustration of a cantilever tip used in theformation of a microbubble or a nanobubble in accordance with an aspectof the present invention;

FIG. 4 is a schematic representation of a cantilever tip configured as ananogenerator in accordance with an aspect of the present invention;

FIGS. 5A-5F illustrate views of a cantilever configured with valves forgas flow in accordance with an aspect of the present invention; and

FIG. 6 shows a variation of the cantilever configuration illustrated inFIGS. 5A-5F.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 shows an SOI (silicon on insulator) MEMS cantilever f100 havinggas channels f101 formed in the device layer. Each channel is fed via arecess f105 (shown in phantom) formed in the body of in the handle layerf103 of the cantilever f100. The recess is therefor in fluidcommunication with the channels f101. Gas introduced through the floorplate or gas feed tube (not shown) from a gas source (not shown) isthereby delivered via the recess f105 to the channels f101 and finallyto a region of the tip at the end of the cantilever f100.

As can be seen in the enlarged view, a cover seal (or cover layer) f104can be provided to contain the gas pressure that can be developed at thetip. In one embodiment, the cover seal can be any suitably patternedthin material including adhesive plastic films, silicon cover structure,or diamond film cover structure. These latter materials may be bonded bycoating with Titanium, Nickel and Copper layers to make a Copper vacuumfurnace bond, or by using conventional low temperature eutectic bondssuch as a Ge/Ag, Ge/Au, In/Pt, In/Pa or In/Ag to a similarly coateddevice layer or other mechanically strong layer sufficient to containthe gas pressures used. This latter cover layer may be disposed so as toreduce the etched gap between the arms and the tip portion of theprimary cantilever and in fact may overlap the cantilever end if it issuitably relieved by etching or other means to have clearance similar oridentical to the clearance between the back of the primary cantileverand the secondary cantilever or a backing beam.

In FIG. 2, a variation of the cantilever structure illustrated in FIG. 1is shown. In this variation of the cantilever f200, venturi structuresf201 (venturi tubes) are formed in a portion of the gas channels f101.Tubes f202 lead away and interconnect to the area of the tip on thecantilever to provide a vacuum that is suitable for special functionssuch as new measurement and material modification means. A vacuumproduced by this configuration may also be used for other purposesincluding a vacuum clamping system which retains the whole assembly(including an attached base plate on the handle layer) onto theinstrument or tool in use.

In FIG. 2 and also in FIGS. 1A and 1B, a fluid (e.g., water) may beplaced in the gas channel or delivered to the gas channel using the samemechanism and pathways as the selected gases described herein. Here asshown in FIG. 3 a tip with a flat end directly proportional in diameterto the desired microbubble or nanobubble to be formed is driven by(typically) a piezoelectric excitation system. The excitation system canbe the same system that is used to excite the cantilever for AFMscanning, for example. The excitation system increases its amplitudesuch that cavitation bubbles are formed at the end of the tip and at aknown distance away from the work surface. These cavitation bubbles maybe used to machine a target surface. The cavitation bubbles can be usedto illuminate, by the sonoluminescence effect, a particular spot on awork piece, or initiate a photo induced reaction into a work piece. Thetarget piece or workpiece can be viable DNA.

The fluid can be withdrawn from the area of the tip using the capillaryaction within the fluid, the maintenance of wetable surfaces in thechannel, and the application of some backpressure on the fluid.Additionally, as shown in FIGS. 1A and 2A, fluid (including gas) may becontinuously removed and replenished or otherwise recirculated afterbeing modified (for example, due to filtering, cooling or heating, orotherwise chemically changed) so as to maintain specific conditions atthe tip and sample. Alternatively, the fluid may be expelled in meteredways from the ends of the gas channel by a pulse pressure.

FIG. 2B is a schematic exploded side view of a holder f201 a and acantilever f102 a received in the holder. A cover seal f104 a is shownseparated from the cantilever f102 a. The holder f201 a is configuredfor fluid flow in the direction shown by the arrows. Fluid enters fromthe right-bottom portion of the holder f201 a, exiting the holder at alocation where the base of the cantilever f102 a is received. Withreference to FIG. 1, the fluid exiting the holder f201 a enters therecess f105 from the base of the cantilever f102 a.

FIG. 2C is a schematic exploded side view of a holder f201 c and acantilever received in the holder. A cover seal f104 c is shownseparated from the cantilever. The holder f201 c is configured forbi-directional fluid flow as shown by the arrows. Fluid enters and exitsfrom the right-bottom portion of the holder f201 c, exiting and enteringthe holder at a location where the base of the cantilever is received.

In another embodiment, chemical, optical and/or electrical means may beprovided through and/or with the tip to perform measurements at the tipregion, or to effect other processes in the region of the tip with orwithout the benefit of fluid or gas delivered to the tip region. One ormore streams of gas and/or fluid delivered to the tip region may also beused to induce reactions or processes suitable to the goals ofmeasurement or process development. Specifically these latter techniquesare well suited to be used with biological or chemical cell assemblies,sometimes referred to as biochips, such as those made by Affymetrix. Ina biochip, the local region of fluid control and/or tip activity issubstantially smaller than the size and volume of the biochip cell.

Furthermore these biochips are commonly caused to fluoresce on theactivated DNA sites and the resulting light emission in conjunction withlight sensitive tips can be used to locate the actual DNA directly. TheDNA can then be removed and moved to another location for furtheroperations. The DNA can be processed on site in the biochip. This lightdriven location would simply consist of monitoring the light received bythe control computer or logic and/or memory and then mapping theregion(s) of maximum and minimum light output for operations to bedirected subsequently by the operator or a computer and or logic and/ormemory based director. Alternately the fluid may be expelled in meteredways from the ends of the gas channel by a pulse pressure.

In still another embodiment, one or more diaphragms (electrostatically,piezoelectrically, or thermally actuated) can be integrated into thecantilever f100 via known MEMS techniques to provide gas flow (such asby applying a vacuum or lower pressure to the channels) or fluid flowthrough the channels from a source of gas or fluid that is provided tothe device. Alternatively, a co-resonant pendulum pump with or withoutvalves (as shown in the views of FIGS. 5A-5F), and/or thermal (pressuredifferential by fluid or gas heating) pumps can be incorporated into thecantilever f100 also using known MEMS techniques to provide gas or fluidto the tip. This aspect of the invention avoids having to directlyconnect the cantilever to an external supply to provide the fluid flowand control. A local and/or MEMS based flow control may also be used toregulate an external supply or server as an additional regulation of thediaphragm or thermal pumps above.

Further the fluid or gas may be further shaped and guided by thearrangement shown in FIG. 1C so that the flow is orthogonal to thecantilever and below the lowest part of the cantilever so that theregion of flow is not in contact with the cantilever. Alternatively, thecantilever shown in FIG. 3, at f301 c, is streamlined to lower itsdamping by the fluid and to eliminate the formation in liquids ofcavitation bubbles from the surfaces orthogonal to its motion.Additionally the channel arms may be movable and can be configured tohave a spring constant such that a sufficiently strong vacuum sourceapplied to the channels causes the arms to mechanically engage the tipplatform. This would mechanically constrain its motion or make it movetoward one channel or the other (the channel in which the vacuum isapplied).

The mechanical constraints are removed when normal or positive pressureis applied to channel(s). By this means, the tip platform may be movedor scanned over the surface or clamped in between the channels alternatemeans well know in the MEMS art may be used to move the channel arms inx, y and z axis including independent thermal, electrostatic andpiezoelectric translation of all or any of the arms. Furthermore, thechannel arms may be arranged to lie over secondary cantilevers (whichare described in more detail in one or more of the above-referencedapplications) such that these cantilevers do not extend to the area ofthe primary cantilever. Instead, when the movable arms are used to clampthe primary cantilever the whole clamped assembly is free to move backuntil each clamp arm of the assembly encounters a secondary cantileverwith a corresponding increase in spring constant from these structures.Furthermore when driven independently, the instant of electrical contactof any given arm with the structure to be clamped can be sensed and usedby an external controller or analog circuit to control the clampingforce and motion of the arm so that a given displacement of the clampedstructure can be obtained (including zero displacement). The motion ofthe arms can also be sensed by conventional piezoelectric andpiezoresistive methods.

Furthermore as shown above in FIG. 2 and FIGS. 1A and 1B, another fluidand in particular a dielectric fluid, like electrical dischargemachining oil (typically, a kerosene like oil well known in the machinetool industry) may be introduced around the work piece (tool form toform a particular shape on the tip by suitably placing a bias voltage—dcoffset ac voltage or simple dc voltage under which workpiece or samplematerial will be removed from the anode whether that is the work pieceor the GN probe see FIG. 3). For this purpose, conductive diamond isespecially appropriate because its ability to conduct away heat reducesits erosion wear substantially. Another useful material is tungsten.

Finally, in either embodiment shown in FIG. 1, 2, or 1C, a conventionalisotope or electrical emitters may be introduced in the main gas channelf105 formed in the handle f103, or in the individual gas channels f101in the device layer via openings f106 a. A further embodiment is to usea total of 0.99 or less microcurie of radioactive material in total (sumof all material applied to the device) in order to meet national andinternational maximums for unregulated transport and use of radioactivematerials.

Another embodiment is to use Americium 241 which is commonly used insmoke detectors as the isotopic source of alpha particles. Theseemitters will form ions in the gas flowing around them which can then beused to charge or neutralize charge around the tip area wheremeasurement or surface modification is taking place. The gas flow ratedetermines the charge transfer rate out of the channels. The gas flowcan be monitored by conventional measuring by techniques the chargeacross the channel through connections. This aspect of the invention isshown in FIG. 4. The voltage is measured at the integration point(connection between the diode and the capacitor) with a resistordischarging the voltage so as to correlate with rate of charge transferand removal by gas flow.

A further embodiment of the nuclear emitter is shown in FIG. 4. Here acomplete nanogenerator is formed in which the electrical energy ofnuclear decay from an isotope at f306 a is captured by conductive layerf301 a which may be in close contact. An intrinsic silicon diode, orintrinsic diamond diode, or intrinsic SiC diode formed by CVD (chemicalvapor deposition) growth of an oriented boron doped diamond layerfollowed by the growth of an intrinsic or ultra pure undoped diamondlayer or diode junction is electrically arranged to provide a current ofsecondary holes or electrons from the ionizing action (attached to thedevice layer which may also be conductive) and insulated from the groundlayer on which the isotope is electrodeposited or affixed at f302 a.This voltage is then integrated by the simple diode and capacitorcircuit shown as f304 a and f305 a.

The diode and capacitor may be integrally formed on the silicon MEMSdevice. In this way, a quantity of current is available for any generaluse by making a connection to the conductor that connects f304 a andf305 a. Many nanogenerator regions may be made and integrated on onedevice such that under normal circumstances no local concentration ofisotopic material will exceed the legally accepted microcurieconcentration per unit area of the device. Furthermore the intrinsicdiode may be spaced away from the radiation source by a hard vacuum andan internal thin metal diaphragm which may be released by the passage ofcurrent through one of its support arms allowing the other support barto roll it up and out of the way of the radiation source. By the lattermeans the generator diode can be protected from radiation damage whilein storage and the storage life can be extended to hundreds of years.

In another embodiment, the intrinsic diamond layer may be grown ormechanically contacted against a doped SiC (silicon carbide) crystalwith a boron doped diamond layer (either random or aligned biased grown)grown on the other side of the intrinsic diamond away from the SiC. Anadditional embodiment includes a conductor followed by an intrinsic SiClayer grown on top of a doped SiC layer. In this and the formerembodiments, these structures may also be used as radiation detectorsfor forms of radiation which give rise to detectable electronic oroptical changes in the layered diode structure.

Yet another embodiment of the above elements includes the provision foractive mechanical and/or electrical actuation of the gas/fluid channels(see above and the drawings of FIG. 6). The channels can be moved intoand away from the tip platform, to act as a clamp or release on theprimary cantilever tip platform. Arm motion may be accomplished by oneor more independent thermal actuators (see FIG. 6), electrostaticactuators, or piezoelectric actuators. The arms may be used to stiffenor immobilize the tip bearing cantilever without the presence or aid ofsecondary cantilevers or beams behind the primary cantilever.

In operation if the tip platform is pressed back to the secondarycantilevers or support beam and the fluid channel is flexed in thechannel cams and locks the platform against the secondary cantilevers orbeam. If on the other hand the tip platform is not pressed back, thenthe edges of the fluid channel wedge under the tip platform and separateit positively from the secondary cantilevers or beam. In operation, thisdesign may include two paddles on long cantilevers within the handlelayer rear fluid channels. These respond to long wavelength modulationof a typical AFM acoustic tip drive to move up and down perpendicular tothe plane of the cantilever assembly and in conjunction with the checkvalves and/or openings depending from the front cover and from thehandle cavities to the two fluid arms act to pump surrounding gas orfluid through the channels over the tip and subject area. The quantityof fluid or ionized gas can be controlled by a software module whichallows the operator to change the duty cycle of the long wave acousticexcitation.

What is claimed is:
 1. A micro electromechanical systems (MEMS) scanningprobe microscopy (SPM) cantilever device for supporting a tip, the SPMcantilever device comprising: a first cantilever portion configured tosupport the tip; and a second cantilever portion distinct from the firstcantilever portion; wherein the second cantilever portion includes oneor more fluidic channels that are spaced from the first cantileverportion to communicate fluid between a region spaced from the tip and aregion proximate the outside of the tip without the fluid passingthrough the tip.
 2. The SPM cantilever device of claim 1 wherein localor integrated pumps and/or valves provide for the delivery and/orcontrol of fluids or gases.
 3. The SPM cantilever device of claim 2wherein the fluid channel also functions as an active mechanical orelectromechanical member.
 4. The SPM cantilever device of claim 2 andfurther comprising one or more movable members that act as passiveelements.
 5. The SPM cantilever device of claim 2 and further comprisingone or more movable members that act as passive elements and areactivated or operated by external mechanical, vacuum, or fluid inducedforces.
 6. The SPM cantilever device of claim 1 wherein: the SPMcantilever device is formed from a silicon-on-insulator (SOI) waferhaving a handle layer and a device layer; the device layer is patternedto provide the first and second cantilever portions; the fluidicchannels are formed in the device layer in portions on either side ofthe first cantilever portion that supports the tip to provide fluidcommunication at the region proximate the outside of the tip; and thehandle layer is formed with one or more recesses in fluid communicationwith the fluidic channels.
 7. A scanning probe microscopy (SPM) assemblycomprising: a cantilever structure; and a tip supported at an endportion of the cantilever structure; wherein, the cantilever structureis formed with one or more fluidic channels that communicate fluidbetween a region spaced from the tip and a region proximate the outsideof the tip, and the fluidic channels are formed without passing throughthe tip.
 8. The SPM cantilever assembly of claim 7 wherein: thecantilever structure is formed from a silicon-on-insulator (SOI) waferhaving a handle layer and a device layer; the device layer is patternedto provide the end portion of the cantilever that supports the tip; thefluidic channels are formed in the device layer in portions on eitherside of the cantilever portion that supports the tip to provide fluidcommunication at the region proximate the outside of the tip; and thehandle layer is formed with one or more recesses in fluid communicationwith the fluidic channels.